<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
<style type="text/css">
img {
    /* 解决div的img图片上下多出三像素问题 */
    vertical-align: middle;
}
.banner {
    width: 100%;
}
.banner img {
    width: 100%;
}
</style>
</head>
<body>
    <div class="banner">
        <img src="http://img04.tooopen.com/images/20130701/tooopen_10055061.jpg">
    </div>
</body>
</html>